Now, this probably seems confusing, at first. How can something so beneficial be so bad? Well, it's simple. Using too wide of an aperture causes things that need to be in focus to be out of focus. Shooting a portrait at ƒ/1.4 and focusing on the closest eye can cause the further eye to be out of focus. Additionally, and probably even worse, are having the eyes in focus while the nose is out of focus.
When shooting portraits, it's very important to have the entire face in focus, not just the eyes. Many photographers, even seasoned pros, sometimes fall into this trap simply because, when doing a portrait session, time is often tight and the photographer first checks to see if the background is pleasing, then typically checks focus on the leading eye and moves on.
It's entirely possible to get a portrait with all elements of your face in focus at ƒ/1.4, as long as you have enough distance between the lens and subject. This is one reason why many professional portrait photographers opt to use an 85mm ƒ/1.4 over a 50mm ƒ/1.4 for headshots. The distance flattens out the facial features, which not only makes them more pleasing, but also ensures they're all in focus.
FINAL TIPSWhether you're shooting a landscape, street scene or a portrait, the most important thing to keep in mind about depth of field is that it's not an either/or situation. You don't need to open all the way up to get super-shallow depth of field or stop down all the way and get everything in focus. Selecting the right aperture to get the perfect balance of sharpness and bokeh to enhance the subject is what this is all about.
J. Dennis Thomas is a freelance photographer and author based in Austin, Texas. He's the author of Wiley Publishing's Nikon Digital Field Guide series, as well as Concert and Live Music and Urban and Rural Decay Photography published by Focal Press. Find him at www.NikonDFG.com and @JDennisThomas on Twitter.